IEEE 802.11ac Gigabit Wi-Fi

- notes and details of the IEEE 802.11ac gigabit Wi-Fi standard to provide data throughput rates of up to 1Gbps at frequencies up to 6 GHz.

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The IEEE802.11ac Wi-Fi standard has been developed to raise the data throughput rates attainable on Wi-Fi networks up to rates of around 1 Gbps. The implementation of Gigabit Wi-Fi is needed to ensure that Wi-Fi standards keep up with the requirements of users.

The new IEEE 802.11 ac Gigabit Wi-Fi standard is in development and is anticipated to be released by about 2012.

IEEE 802.11ac Gigabit Wi-Fi highlights

The IEEE 802.11ac Gigabit Wi-Fi standard utilises a number of techniques that have been utilised within previous IEEE 802.11 standards and builds on these technologies, while adding some new techniques to ensure that the required throughput can be attained.

• OFDM:   The IEEE 802.11ac standard utilises OFDM that has been very successfully used in previous forms of 802.11. The use of OFDM is particularly applicable to wideband data transmission as it combats some of the problems with selective fading.
  
  

  Note on OFDM:

  Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each another there is no mutual interference. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period. This means that when the signals are demodulated they will have a whole number of cycles in the symbol period and their contribution will sum to zero - in other words there is no interference contribution. The data to be transmitted is split across all the carriers and this means that by using error correction techniques, if some of the carriers are lost due to multi-path effects, then the data can be reconstructed. Additionally having data carried at a low rate across all the carriers means that the effects of reflections and inter-symbol interference can be overcome. It also means that single frequency networks, where all transmitters can transmit on the same channel can be implemented.

  Click on the link for an OFDM tutorial

  
  
• MIMO and MU-MIMO:   In order to achieve the required spectral usage figures to attain the data throughput within the available space, the spectral usage figure of 7.5 bps/Hz is required. To achieve this, MIMO is required, and in the case of IEEE 802.11ac Wi-Fi, a form known as Multi-User MIMO, or MU MIMO is implemented.
  
  

  Note on MIMO:

  Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.

  Click on the link for a MIMO tutorial

  
  
  MU-MIMO enables the simultaneous transmission of different data frames to different clients. The use of MU-MIMO requires that equipment is able to utilise the spatial awareness of the different remote users. It also needs sophisticated queuing systems that can take advantage of opportunities to transmit to multiple clients when conditions are right.
• Error correction coding:   The advances in chip manufacturing technology have enabled designers to take advantage of additional levels of processing power when compared to previous implementations of the 802.11 standards. This has enabled the use more sensitive coding techniques that depend on finer distinctions in the received signal. IN addition to this more aggressive error correction codes that use fewer check bits for the same amount of data have been utilised within the 802.11ac format
• Increased channel bandwidth:   The previous versions of 802.11 standards have typically used 20 MHz channels, although 802.11n used up to 40 MHz wide channels. The 802.11ac standard uses channel bandwidths up to 80 MHz. To achieve this it is necessary to adapt automatic radio tuning capabilities so that higher-bandwidth channels are only used where necessary to conserve spectrum

The IEEE 802.11ac Gigabit Wi-Fi offers significant advantages over the previous incarnations of the 802.11 standard. It offers backwards compatibility with previous versions and this will enable it to be introduced in the existing Wi-Fi ecosystem with the minimum of disruption.

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